Field of the Invention
Aspects of the present invention relate to a power supply apparatus for wirelessly supplying power to an external apparatus.
Description of the Related Art
In wireless power transmission, an antenna (a power receiving antenna) of a power receiving apparatus on a power receiving side receives an electromagnetic wave emitted from an antenna (a power transmission antenna) of a power transmission apparatus on a power transmission side. Electric power is thereby transmitted from the power transmission apparatus to the power receiving apparatus. It is not desirable that the power transmission apparatus emit the electromagnetic wave conveying the electric power in an uncontrolled state. Therefore, in general, the power transmission apparatus and the power receiving apparatus acquire power transmission/reception information from each other by communication prior to the wireless power transmission, and then the power transmission apparatus emits, from the antenna, an electric power wave of power determined according to the power transmission/reception information.
When carrying out such wireless power transmission, it is necessary to give consideration to preventing the electric power wave emitted from the power transmission antenna, from exerting influence such as heat on a contactless IC card or the like which is unintentionally brought nearby. Assume that the frequency of the electric power wave emitted from the power transmission antenna is, for example, about 13.56 MHz in the high frequency (HF) band. In this case, a contactless IC card equipped with an antenna having a resonance frequency of about 13.56 MHz can receive notable influence such as heat exerted by this electric power wave. Further, assume that the frequency of the electric power wave emitted from the power transmission antenna is, for example, about 6.78 MHz in the HF band. Even in this case, it is not possible to avoid adverse influence such as heat generation on the contactless IC card equipped with the antenna having the resonance frequency of about 13.56 MHz that is twice as high as 6.78 MHz.
Japanese Patent Application Laid-Open. No. 2006-42519 discusses a wireless power transmission system including a transmission apparatus having a first plane coil, and a power receiving apparatus having a second plane coil. In this system, a magnetic sheet is provided on each of surfaces opposite to the respective surfaces facing each other of the first plane coil and the second plane coil.
Japanese Patent Application Laid-Open No. 11-224822 discusses a contactless power supply apparatus for wirelessly transmitting electric power from a primary side to a secondary side, by magnetizing a power supply line on primary side. In this apparatus, a harmonic current flowing through the power supply line on the primary side is reduced by changing an output voltage waveform of a high frequency inverter in two or more stages. In the configuration discussed in Japanese Patent Application Laid-Open. No. 2006-42519, unnecessary radiation from the coil is suppressed by the magnetic sheet, but influence caused by a change in an operation state or usage state is not considered. In a case of tight coupling such as electromagnetic induction, the configuration discussed in Japanese Patent Application. Laid-Open. No. 2006-42519 is effective. However, in a case of loose coupling such as magnetic resonance for transmitting the electric power, it is difficult to suppress radiation of a magnetic field.
The harmonic component included in the electric power wave is also influenced by a change in operation state or usage state of an apparatus that is present outside the power transmission apparatus. However, such influence is not taken into consideration in the harmonic current suppression discussed in Japanese Patent Application Laid-Open No. 11-224822, and an intended effect thereof is not obtained in some cases.
Therefore, the configuration discussed in each of Japanese Patent Application Laid-Open Nos. 2006-42519 and 11-224822 cannot reduce the possibility that the electric power wave emitted from the power transmission antenna may exert adverse influence such as heat generation on the nearby contactless IC card.